1. Field of the Invention
The invention relates to a key switch comprising a casing, at least one key slide guided in the casing against the force of a spring and at least one J-shaped leaf spring having a long spring arm and a short spring arm connected to the long arm by a curved intermediate part, said leaf spring being clamped to assume a unilateral curvature between two abutments, one of which is movable relative to the other, and having the free end of its long spring arm supported in a first abutment in the key slide and its curved intermediate part in a second abutment of a fixed contact member provided in the casing.
2. Brief Description of the Prior Art
Key switches of this kind in multiple unit arrays are required, for instance, for key assemblies for switching in the individual channels of high frequency receivers, such as radio and television receivers. By means of a single key-pressing operation the respective preset tuning voltage and thus the associated station or channel, can be switched in. Storage of the set tuning voltage takes place in the channel memory in the form of spindle-type resistors or variable resistors connected as voltage dividers.
A key switch in connection with a key assembly is already known, wherein the key switch consists of a narrow elongated switching rod guided in the front and rear walls of the casing. The switching rod has a plurality of integrally formed shoulders on its underside. On the bottom of the casing contact bars are mounted tranversely to the switching rods, which among other elements comprise a connecting member and a number of U-shaped spring elements corresponding to the number of switching rods. One end of each spring element is fastened to the connecting member, whereas the free end cooperates with the shoulders of the switching rod.
When any one of the switching rods is pressed, the free end of the spring element is urged against the respective associated wire contact by means of the shoulders. The spring elements accordingly serve simultaneously as return springs for the switching rods and as electrical connectors. The spring elements are subject to bending as well as torsional stress in the closed circuit condition.
Furthermore, a key switch is already known, wherein a push rod is adapted to slide against the force of a return spring. The snap spring and the contact arm are formed integrally and are of J-shaped configuration. With its curved intermediate part the spring is pivotally supported in a fixed contact member. The free end of the long spring arm is supported in a knife-edge bearing of the push rod. The long spring arm thus is clamped between two abutments to define a unilateral curvature. The short spring arm serves as contact arm and carries a contact rivet. In one embodiment two snap springs are arranged on both sides of the push rod, and furthermore the push rod additionally comprises a supporting member mounted for sliding up and down in the sliding direction of the push rod. When the push rod is pressed down, the return spring is compressed and at the same time the two snap springs are pivoted and tensioned. As soon as the dead centre position is reached, the snap springs suddenly snap into the ON position, while the supporting member moves relative to the push rod. It is a condition for this switching mechanism that the snap springs be arranged symmetrically and almost perpendicularly to the sliding direction of the push rod. Because of this condition, very much space is occupied in the lateral direction.